There’s often a lot of confusion when we try to discuss how to calculate the number calories you burn every day. A lot of different terms get used sometimes interchangeably, which may be incorrect depending on the method that we calculate the number of calories the body burns every day.
What is Basal Metabolic Rate (BMR)?
Basal metabolic rate, also called BMR, is one of the more basic and common physiology terms people read about when trying to figure out their calories for weight loss. The basal metabolic rate (BMR) measures the amount of energy required by your body for essential functions such as breathing and your heart beating. Basically, anything your body needs to do to keep you alive while at rest.
How is BMR measured?
BMR can be most accurately measured in a laboratory setting. Laboratory measurement of BMR usually requires spending the night sleeping in the lab and then first thing in the morning while still in bed, having your basal metabolic rate measured. Obviously it’s a fairly complicated and involved process for most people, but laboratory determination of BMR is a very accurate test.
Other ways to calculate BMR
Fortunately, scientists have figured out a few formulas and calculations to estimate your basal metabolic rate without having to spend the night and physiology lab.
Harris-Benedict BMR Equation
The Harris-Benedict basal metabolic rate equation was first published in 1918 by J. Arthur Harris and Francis G Benedict as the first attempt to try to develop a formula to calculate a person’s BMR based on their prior laboratory results. The Harris-Benedict BMR equation requires the height, weight, age and sex of the person to calculate their basal metabolic rate
|Harris-Benedict BMR equation (Imperial units)
|BMR = 655 + ( 4.35 × weight in pounds ) + ( 4.7 × height in inches ) – ( 4.7 × age in years )
|BMR = 66 + ( 6.2 × weight in pounds ) + ( 12.7 × height in inches ) – ( 6.76 × age in years )
|Harris-Benedict BMR equation (Metric units)
|BMR = 655 + ( 9.563 × weight in kg ) + ( 1.850 × height in cm ) – ( 4.676 × age in years )
|BMR = 66.5 + ( 13.75 × weight in kg ) + ( 5.003 × height in cm ) – ( 6.755 × age in years )
Modified Harris-Benedict BMR Equation
The modified Harris-Benedict BMR equation was published in 1984 and revised and updated the original Harris-Benedict equation based on new data collected over the previous 60 years. This updated basal metabolic rate equation found that the calculation was within 200 calories a day of actual laboratory testing of a person’s BMR.
|Modified Harris-Benedict BMR equation (metric units)
BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) – (4.330 × age in years)
BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) – (5.677 × age in years)
Mifflin-St Jeor BMR Equation
The Mifflin-St Jeor basal metabolic rate equation was published in 1990 as another update to the original and modified Harris-Benedict BMR equations. Mifflin and St Jeor found that the original Harris-Benedict BMR equation overestimated a person’s basal metabolic rate by about 5 percent. For a male with a BMR of Harris-Benedict BMR calculation of 2000 calories a day, the Mifflin-St Jeor equation would calculate a BMR closer to 1900 calories a day.
|Mifflin-St Jeor BMR equation (metric units)
|BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
Which BMR equation is most accurate?
Currently, the Mifflin-St Jeor basal metabolic rate equation is believed to be the most accurate BMR calculation. Although all the BMR equations are limited since they do not differentiate between lean body mass and fat mass. A heavier person who is obese will find that their calculated BMR with these formulas is higher that their true basal metabolic rate.
You can calculate your Basal Metabolic Rate with our basal metabolic rate calculator.
How to get your BMR tested?
True BMR testing with an overnight in a physiology lab is not the easiest test to get done for most people looking to find out their basal metabolic rate. However, many gyms and fitness centers offer Resting Metabolic Rate testing which is somewhat similar to Basal Metabolic Rate testing.
The difference between BMR and Resting Metabolic Rate (RMR)
Resting Metabolic Rate testing is a more “informal” measurement of how many calories your body burns at rest. A true BMR or basal metabolic rate test is done first thing in the morning after sleeping overnight in a testing lab. BMR is also tested after a 12 hour fast.
Unlike BMR testing, the resting metabolic rate (RMR) testing can be done anytime during the day and typically only requires you not to eat for four hours prior to the test. Both tests usually require wearing a face mask connected to a machine that measures the amount of oxygen and carbon dioxide as you inhale and exhale. By measuring these values, the machine can calculate the number of calories your body burns each day.
Some university physiology or sports medicine departments will offer Resting Metabolic Rate testing. There are also some commercial companies like BodySpec and Body-Comp that also offer Resting Metabolic Rate testing.
Why get your BMR or RMR tested?
BMR or RMR testing is not a requirement for a weight loss program, but it can be helpful to have an understanding of how many calories your body uses at rest. However, you should then also calculate your TDEE or Total Daily Energy Expenditure to determine how many calories you burn each day with normal daily activities and with any exercise.